Electromagnet and permanent magnet

Electromagnets and permanent magnets have been widely used in many applications. Permanent magnets such as bar magnets have been used in hard disk drives, vehicles and magnetic hooks. Electromagnets such as coils are most commonly used in transformers and various medical equipment. In some applications, electromagnets and permanent magnets have been used together. What is the main difference between electromagnet and permanent magnet? How do we choose the right for our application?

Permanent magnets are made of strong magnetic hard materials, which can maintain their magnetism without external stimulation. Due to the strong magnetism of materials such as neodymium, iron and boron, permanent magnets are a perfect choice, which can produce a consistent strong force to attract other objects at close range. When two magnets stick together, the force between two 8cm NdFeB cube magnets can easily reach 5K Newton. In many applications, such as magnetic hooks, permanent magnets can provide long-term grip without any additional energy input.

On the other hand, the disadvantage of permanent magnet is also caused by its material characteristics. Because these magnets maintain their magnetism, they can never close or control force when their relative position is fixed. This makes them difficult to apply to applications that require varying forces. The force of the permanent magnet becomes ineffective for long distances because the force decays with the distance cube. It may be noted that when the distance increases from 0 cm to 10 cm, the force between two 8 cm NdFeB magnets decreases rapidly from 5K to 100 Newtons. Finally, permanent magnetic fields can only be generated below a certain temperature, so they are not suitable for thermal device applications.

Electromagnets are like the opposite side of permanent magnets. The magnetic field is generated by the current flowing through the solenoid. The magnetism of the coil depends on the current flowing through the wire. Because of this characteristic, electromagnet is the most commonly used type in applications requiring rapid change of magnetic field or precise control of magnetic field. An example is that in MRI, it is usually necessary to create an accurate field / field gradient at a specific position in space. By changing the current in different coils, it is easy to realize the accurate control of space magnetic field, which is almost impossible to obtain the same results by using permanent magnets. By using different current inputs, a complex and real-time magnetic field arrangement can be created through the coil.

The main disadvantage of electromagnet is energy transmission. Although the permanent magnet is pre magnetized and does not need energy input in the application process, the electromagnet needs a constant current source. Compared with permanent magnets, this feature makes electromagnets much less efficient in generating strong magnetic force at close range. Due to the different variables related to current source interference and heating, compared with permanent magnets, electromagnets need to be more careful in design and maintenance to maintain high-precision magnetic field output.